1. Field of the Invention
The present invention relates to wireless communications and, more specifically, to wireless relay networks.
2. Description of the Related Art
A wireless relay network is a multi-hop system in which end nodes, such as mobile stations (MS) and subscription stations (SS) are connected to the base station (BS) or access point (AP) via a relay station (RS). The traffic between the MS/SS and the BS/AP passes through and is processed by the relay station (RS).
The 802.16 Mobile Multi-Hop Relay (MMR), a study item established in the IEEE 802.16 working group, provides examples of relay networking. The MMR working group focuses on defining a network system that utilizes relays stations (RS) to extend the network coverage and/or enhance the system throughput. FIG. 1 illustrates an exemplary relay network which comprises, in part, a relay station (RS), mobile station (MS), subscriber station (SS) and base station (BS).
Hybrid automatic repeat request (H-ARQ) is a scheme which combines ARQ protocols with forward-error-correcting (FEC) schemes that are generally considered to be the best error-control techniques for wireless links. Different wireless technology may have different H-ARQ schemes.
In IEEE 802.16, the H-ARQ scheme is implemented as a part of the media access controller (MAC) and can be enabled on a per-terminal basis. Two main variants of H-ARQ are supported: chase combining and incremental redundancy (IR). For IR, the PHY layer encodes the H-ARQ generating four versions for the encoded H-ARQ attempts. Each H-ARQ attempt is uniquely identified using a H-ARQ attempt identifier (SPID). For chase combining, the PHY layer encodes the H-ARQ packet generating only one version of the encoded packet. As a result, no SPID is required for chase combining.
For downlink operation, the BS sends a version of the encoded H-ARQ packet to the MS/SS. The MS/SS attempts to decode the encoded packet on this first H-ARQ attempt. If the decoding is successful, the MS/SS sends an acknowledgement (ACK) to the BS. If the decoding is not successful, the MS/SS sends a non-acknowledgement (NAK) to the BS. In response, the BS will send another H-ARQ attempt to the MS/SS. The BS may continue to send H-ARQ attempts until the MS/SS successfully decodes the packet and sends an ACK.
The H-ARQ scheme works well in a system without a relay station (RS) where the H-ARQ scheme is applied directly between the BS and MS/SS. However, when a RS is introduced into the system, although H-ARQ is still implemented between the MS/SS and BS, the RS needs to forward all the H-ARQ attempts and ACK/NAKs between the MS/SS and BS.
Therefore, according to prior art solutions, if the first H-ARQ attempt is not sent successfully due to error or loss, another H-ARQ attempt needs to be sent until the MS/SS or BS successfully decodes it. Consequently, the subsequent H-ARQ attempt(s) must be transmitted over all the different hops (links) between the BS and MS/SS. Bandwidth is re-allocated between BS and MS/SS for transmitting the subsequent H-ARQ attempt(s), even though some of the links may have already transferred the frame successfully. This results in bandwidth wastage and throughput loss. Thus, there is a need for an enhanced H-ARQ scheme with an improved utilization of network resources.
In view of the above, embodiments of the present invention provide an improved H-ARQ scheme which provides better bandwidth utilization. The invention can be applied to relay in various wireless technologies, such as WiMax MMR.